What is AdBlue? Cost, where to buy it and how to top it up (UK guide)
AdBlue is a fluid that many modern diesel cars use to cut harmful exhaust emissions. It goes in its own separate tank, costs roughly £10 to £20 for a 10-litre container, and you can usually top it up yourself in a few minutes. If it runs out, most cars will reduce power and then refuse to restart.
This guide explains what AdBlue is, which cars need it, how much it costs, how to top it up safely, what the warning lights mean, and what to do if you run out.
Last updated 29 September 2026. Usage figures come from the AA and RAC. Prices vary between retailers, so always check before you buy.
Key takeaways
- AdBlue is used by many newer diesel cars, not by petrol or electric cars. It has its own tank and filler cap.
- A car may use roughly a litre every 350 to 600 miles, so a top-up is typically needed every 3,000 to 12,000 miles.
- You will usually get a warning when around 1,500 miles of AdBlue remain.
- If it runs out, the car may lose power and will not restart once switched off.
- A 10-litre container typically costs around £10 to £20, which is much less than most dealer prices per litre.
- Never put AdBlue in the diesel tank, and never put diesel in the AdBlue tank.
In this guide
- What is AdBlue and what does it do?
- How much AdBlue does a car use?
- What do the AdBlue warning lights mean?
- How much does AdBlue cost?
- How to top up AdBlue yourself
- What happens if you run out of AdBlue?
- Why is the AdBlue light on when the tank is full?
- Frequently asked questions
- Sources and further reading
What is AdBlue and what does it do?
AdBlue is a clear liquid made from urea and water. Many modern diesel cars spray it into the exhaust as part of a system called selective catalytic reduction (SCR), where it helps turn harmful nitrogen oxide (NOx) gases into harmless nitrogen and water. It is not a fuel additive, and it is not mixed with diesel. It has its own tank and its own filler cap.
Not every car needs it. AdBlue is used mainly in newer diesel cars, including many Euro 6 models built from around 2015. Petrol cars and electric cars do not use it. Manufacturers use different names, such as SCR, BlueHDi (Peugeot and Citroën) or BlueInjection (Vauxhall), so check the handbook or look for a separate, usually blue, filler cap next to the diesel cap, in the boot or under the bonnet.
How much AdBlue does a car use?
Consumption varies by car, engine and driving style. The AA says a car might use about a litre every 600 miles or so, but it could be as high as a litre every 350 miles, and that most drivers will need to top up at least once between normal services.
| Measure | Typical figure |
| Consumption | Roughly 1 litre every 350 to 600 miles, depending on the car |
| Tank size | Commonly 10 to 20 litres, depending on the model |
| Refill interval | Anywhere from about 3,000 to 12,000 miles, according to the AA |
| First warning | Usually when around 1,500 miles of AdBlue are left |
| Litres to restart after running empty | The AA suggests about 5 litres should be enough, but check your handbook |
Worked example: if your tank holds 12 litres and your car uses a litre every 500 miles, a full tank lasts about 6,000 miles. If you cover 10,000 miles a year, you would top up roughly twice a year. Your handbook gives the tank size and the manufacturer’s figures.
What do the AdBlue warning lights mean?
Your car warns you in stages, and the exact behaviour differs between manufacturers. The pattern below is typical, but read your handbook for your model.
| Stage | What you usually see | What to do |
| Low level | An AdBlue warning light or message, often with a mileage countdown starting at around 1,500 miles | Top up soon. The car should drive as normal |
| Very low | The countdown gets shorter and warnings become more urgent. Some cars limit performance | Top up as soon as possible |
| Empty | Reduced power on some cars, and the engine will not restart once you switch it off | Add AdBlue before switching off, or call for help |
| Light stays on after a top-up | A possible fault in the SCR system, such as a sensor or pump | Book a garage. See our guide to dashboard warning lights |
The AA says that if you run out while driving, engine power and performance may be reduced to limit emissions, and that you will not be able to restart the engine once the tank is empty. Some manufacturers also cap the car’s speed as the level gets critically low.
How much does AdBlue cost?
Prices vary between retailers, so treat the figures below as a guide.
| Where you buy it | Typical price |
| 10-litre container from a supermarket, motor factor or fuel station | Roughly £10 to £20. The RAC quotes about £15 to £20 |
| Forecourt AdBlue pump, where available | Often cheaper per litre than small bottles, but prices vary by station |
| Main dealer | The RAC says dealers may charge around £2.50 to £4 a litre |
AdBlue degrades over time, so there is little point stockpiling it. The RAC notes that unused solution deteriorates, and many manufacturers advise against keeping top-up bottles in the car. If you are having a service anyway, ask whether the garage checks and tops up AdBlue and how much they charge. Our guides to what a car service includes and how much a car service costs explain what to expect.
How to top up AdBlue yourself
Yes, you can top up AdBlue yourself on most cars. The AA says the filler cap is typically next to the diesel filler cap, but on some cars it is in the boot or under the bonnet.
- Park on level ground and switch the engine off.
- Find the AdBlue filler cap, which is often blue, and check the handbook for the tank size.
- Use AdBlue that meets the ISO 22241 standard, sold in containers with a built-in spout.
- Pour in slowly, and stop when you reach the recommended amount. Do not overfill.
- Wipe up any spills straight away with water, because dried AdBlue can crystallise.
- Refit the cap, start the engine, and expect the warning to clear after a short drive.
Never pour AdBlue into the diesel tank, and never put diesel into the AdBlue tank. Either mistake can cause serious and expensive damage. If it happens, do not start the engine, and call a breakdown service. Our article on what happens if you put the wrong fuel in a car explains more. Some cars have filler points that are awkward to reach or need a garage, so check the handbook if you are not sure.
What happens if you run out of AdBlue?
- Do not switch the engine off until you have AdBlue to add, if you can help it, because the car may not restart.
- Buy AdBlue from the nearest fuel station or motor shop, or call a breakdown service.
- Add the amount your handbook says is needed to restart, which may be several litres.
- If the car still will not start, or the warning does not clear, get help rather than repeatedly trying.
If you are stranded, our guide on why a car will not start covers other causes, and it is a good example of why breakdown cover is a must-have for every driver.
Why is the AdBlue light on when the tank is full?
If the warning light stays on after a top-up, or comes on when the tank is full, the AdBlue system may have a fault. Common causes include:
- A faulty AdBlue level sensor
- A NOx sensor fault
- A failing AdBlue pump or injector, or crystallised AdBlue blocking the system
- Poor-quality or contaminated AdBlue
- Frozen AdBlue in very cold weather. AdBlue freezes at around −11°C, and most cars have a heater to deal with it
Have a garage diagnose it rather than guessing. Do not be tempted to disable the system: removing or bypassing emissions equipment can fail an MOT and may be illegal for road use. Our guides on driving with the DPF light on and DPF cleaning costs cover another common diesel emissions issue.
Frequently asked questions
Can I put AdBlue in my diesel tank?
No. AdBlue has its own separate tank and must never be poured into the diesel tank. If you do, do not start the engine, and call a breakdown service or garage.
Do petrol cars and electric cars need AdBlue?
No. AdBlue is used by diesel engines with an SCR emissions system. Petrol cars and electric cars do not use it.
Can I drive with the AdBlue warning light on?
Usually yes for a while, but you should top up as soon as you can. If you leave it, the car may reduce power and will not restart once the tank is empty.
How much AdBlue do I need to restart after running out?
It depends on the car. The AA suggests about 5 litres should be enough to get the car restarting, but check your handbook.
Does a car service include an AdBlue top-up?
Many services check the AdBlue level and some top it up, but this varies between garages and manufacturers, and dealers may charge a premium. Ask before you book.
Does AdBlue freeze?
Yes, at around minus 11 degrees Celsius. Most cars have a heater in the system so the fluid thaws quickly, but a fault in the heater can trigger a warning in very cold weather.
How long does AdBlue last?
AdBlue degrades over time, especially in heat and sunlight, so buy what you need and keep unused containers cool and out of direct sun rather than stockpiling.
Is AdBlue dangerous?
It is not petrol or fuel and is generally safe to handle, but it can irritate skin and eyes. Rinse spills off skin with water and wipe up drips from the car.
Sources and further reading
- RAC Drive: What is AdBlue? Why does your car need it?
- The AA: What is AdBlue?
- BuyaCar: What is AdBlue?
About this guide: Rooster is a UK car insurance provider. This guide is general information for UK drivers and is not a substitute for your car’s handbook or advice from a qualified mechanic. Consumption, tank size and warning behaviour differ between models.
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